U.S. Pat. Nos. 6,503,141 and 6,743,091 of Meneely, Jr. describe carbon monoxide venting systems using an exhaust blower or fan triggered by a CO detector or sensor.
Air quality sensors for a wide variety of contaminants are available. For example, combustible gas detectors, CO sensors and radon detectors are available for internet purchase on the Promo-Life web site. Other sensors for ammonia and smoke are also commonly available.
Whole house or commercial establishment fresh air ventilation systems are also available. They typically employ at least two blowers, one for removing stale indoor air to the outside of the building and a second blower to replace the removed stale air with fresh air from the outside. They have plenums and ducts for air distribution, heat exchangers to reduce energy loss from the conditioned indoor air being exhausted by preconditioning the replacement outdoor air, filters, and perhaps even electronic air purifiers. These systems can be run continuously, set and run manually, run on a preset intermittent schedule, or controlled by a humidistat. The blower speed, and hence the air exchange rate, are usually settable.